As a seat back frame of a vehicle seat, there is known a seat back frame which is assembled in a substantially inverted U shape in a front view along an outer peripheral portion of a seat back (JP-A-2002-337585). Specifically, the seat back frame is assembled in a substantially inverted U shape in a front view by a pair of left and right side frames made of vertically elongated steel plate material and an upper pipe made of a circular steel pipe and bridged between upper end portions of the respective side frames. The upper pipe is configured to be bent in a substantially inverted U shape in a front view. Bent end portions on both sides of the upper pipe are fitted, from the inside, to fitting portions which are formed at the upper end portions of the respective side frames and are narrowed into a semicircular shape and are welded to the fitting portions.
In the above-described technology, the end portions of the upper pipe bent downward are in contact with the upper end portions of the respective side frames from the lateral side. Therefore, a lap margin in a height direction between the upper pipe and respective the side frames is large, and therefore, the weight is increased.